CARLSBAD, Calif. (AP) — About 4 miles off the coast of Southern California, a company is betting it can solve one of desalination’s biggest problems by moving the technology deep below the ocean’s surface.
OceanWell’s planned Water Farm 1 would use the ocean’s natural pressure to power reverse osmosis — a process that forces seawater through membranes to filter out salt and impurities — and produce up to 60 million gallons (nearly 225 million liters) of fresh water daily. Desalination is energy-intensive, with factories worldwide producing between 500 and 850 million tonnes of carbon emissions annually – approaching the roughly 880 million tonnes emitted by the entire global aviation industry.
OceanWell claims its approach at depth — 1,300 feet (400 meters) below the water’s surface — would cut energy use by about 40 percent compared to conventional plants, while also addressing other major environmental problems that plague traditional desalination: highly concentrated brine discharged back into the ocean, where it can harm, including systems that trap seafloor and coral-bed habitats, killing fish and coral habitats. corals. larvae, plankton and other organisms at the base of the marine food web.
“The world’s freshwater future will come from the ocean,” said OceanWell CEO Robert Bergstrom. “And we’re not going to ask the ocean to pay for it.”
It’s an ambitious promise at a time when the world desperately needs alternatives. As climate change exacerbates droughts, disrupts rainfall patterns and fuels wildfires, more regions are turning to the sea for drinking water. For many countries, particularly in the arid Middle East, parts of Africa and Pacific island countries, desalination is not optional – there simply isn’t enough fresh water to meet demand. More than 20,000 factories now operate worldwide, and the industry has expanded by about 7% annually since 2010.
“With increasing aridity and climate change issues, desalination will become more and more widespread as a key technology globally,” said Peiying Hong, a professor of environmental science and engineering at King Abdullah University of Science and Technology in Saudi Arabia.
But scientists warn that as desalination increases, the cumulative damage to coastal ecosystems – many already under pressure from warming waters and pollution – could intensify.
A search for solutions
Some companies are powering plants with renewable energy, while others are developing more efficient membrane technology to reduce energy consumption. Others are moving the technology entirely underwater. Norway-based Flocean and Netherlands-based Waterise have tested subsea desalination systems and are working towards commercial deployment. Beyond Southern California, OceanWell has signed an agreement to test its system in Nice, France—another region experiencing intense droughts and wildfires—starting this year.
For now, its technology remains in development. A single prototype is operating in Las Virgenes Reservoir, where the local water district has partnered with the company in hopes of diversifying its water supply. If successful, the reverse osmosis pods would eventually float above the seabed in Santa Monica Bay, anchored with a minimal concrete footprint, while an underwater pipeline would carry fresh water to shore. The system would use screens designed to keep out even microscopic plankton and produce less concentrated brine discharge.
Gregory Pierce, director of UCLA’s water resources group, said deep desalination looks promising from an environmental and technical standpoint, but the real test will be cost.
“It’s almost always much bigger than you project” with new technologies, he said. “So I think that will be the starting point of the technology.”
Las Virgenes Reservoir serves approximately 70,000 residents in western Los Angeles County. Almost all of the water comes from the northern Sierra Nevada and is pumped about 400 miles (640 kilometers) over the Tehachapi Mountains—a journey that requires massive amounts of energy. In years of low precipitation and snow in the Sierra, the reservoir and the communities it serves suffer.
California’s Desalination Dilemma
About 100 miles (160 kilometers) up the coast, the Carlsbad Desalination Plant has become a focal point in the state’s debate over the environmental trade-offs of desalination.
The plant became operational in 2015 as the largest seawater desalination facility in North America. Capable of producing up to 54 million gallons (204 million liters) of drinking water daily, it supplies about 10 percent of San Diego County’s water—enough for about 400,000 households.
In Southern California, intensifying drought and wildfires have highlighted the region’s precarious water supply. Agricultural expansion and population growth have depleted local groundwater supplies, leaving cities dependent on imported water. San Diego imports about 90 percent of its supply from the Colorado River and northern California — sources that are becoming increasingly strained by climate change. Desalination was presented as a solution: a local, drought-resistant source of drinking water drawn from the Pacific Ocean.
But environmental groups have argued that the plant’s seawater intake and brine discharge pose risks to marine life, while high energy demands drive up water bills and exacerbate climate change. Before the plant went into operation, environmental organizations filed more than a dozen legal challenges and regulatory disputes. Most were rejected, but some resulted in changes to the design and permits.
“It sucks up an enormous amount of water, and with it sea life,” said Patrick McDonough, a senior attorney at San Diego Coastkeeper, who has participated in multiple legal challenges to the project. “We’re not just talking about fish, turtles, birds, but larvae and spores – whole ecosystems.”
A 2009 order from the Regional Water Quality Control Board estimated that the plant would trap about 10 pounds (4.5 kilograms) of fish per day and required that those impacts be offset by restoring wetlands elsewhere. Seventeen years later, that restoration remains incomplete. And a 2019 study found that the plant’s brine discharge increases salinity in the sea above permitted levels, although it detected no significant biological changes — likely because the site had already been heavily altered by decades of industrial activity from a neighboring power plant.
These impacts are particularly acute in California, where approximately 95 percent of coastal wetlands have been lost largely to development, leaving lagoons as vital habitats for migratory fish and birds.
“When we start messing with these very critical and unfortunately rare coastal lagoons and wetlands, it can have a tremendous impact on the ocean,” McDonough said.
Michelle Peters, chief executive of Channelside Water Resources, which owns the facility, said the facility uses large organism exclusion devices and one-millimeter screens to minimize the uptake of marine life, although she acknowledged that some smaller species can get through.
The plant dilutes its brine discharge with additional seawater before releasing it back into the ocean, and years of monitoring have shown no measurable impact on surrounding marine life, she said.
Peters said the Carlsbad plant has significantly reduced its energy use through efficiency improvements and is operating under a plan to make the facility carbon neutral.
Many experts say water recycling and conservation should come first, noting that wastewater purification typically uses much less energy than seawater desalination and can substantially reduce the impact on marine life. Las Virgenes is pursuing a wastewater reuse project alongside its desalination partnership.
“What we’re looking for is a source of water that we can rely on when Mother Nature doesn’t deliver,” said Pedersen of Las Virgenes. “Developing new local water sources is really a critical measure to be more drought and climate prepared.”
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